The British Fertility Society (BFS) has issued new guidelines for the use of PGS (preimplantation genetic screening) in patients undergoing fertility treatment. The new guidelines, published in the journal Human Fertility, state that there is no evidence that PGS improves pregnancy rates or decreases miscarriage rates for women over the age of 35. They suggest it should only be offered to patients in the setting of a robust clinical trial.

PGS involves removing a single cell from an IVF embryo and testing it for the presence of chromosomeaneuploidies - genetic errors involving excess numbers of a particular chromosome (which are normally in pairs) that would prevent normal embryo development. Only embryos with the correct number of chromosomes are subsequently implanted back into the womb. It has previously been suggested that the technique increases success rates for IVF in women aged over 35, or those who have suffered repeated IVF failure or recurrent miscarriage. The new guidelines were issued after a thorough review of the published research into the use of PGS. They state that clinical trials carried out to date show that live birth rates may be significantly reduced following PGS treatment. PGS is distinct from PGD (preimplantation genetic diagnosis), where embryos are screened for a specific genetic disorder, and the guidelines do not discourage the use of PGD.

It is possible that PGS may be beneficial under certain circumstances, for example where the number of embryos replaced is strictly limited. However, there is no data as yet to support this. The guidelines recommend that clinicians should inform their patients that there is no evidence that PGS improves their likelihood of becoming pregnant and in some cases may result in a reduced chance of pregnancy.

The use of PGS is licensed by the Human Fertilisation and Embryology Authority (HFEA), and currently under 200 women per year receive the treatment. Commenting on the new guidelines, Professor Richard Anderson, from the Centre for Reproductive Biology at the University of Edinburgh and author of the BFS guidelines said that 'there is now an urgent need for further research on PGS to assess both its safety and efficiency in treating a range of patients'.

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